Texture appears stretched on extruded sections of mesh
This can happen for several reasons, the most common being that you modified the mesh after initially adding the texture, hence the stretched look. A simple fix is to just unwrap the model again.
The fastest way to get a good result with a generic box model like that is to press U &gt; Cube Projection or Smart UV Project depending on how tiled you want certain subdivided parts to look (can read more and experiment with the unwrapping types here).
Extrusions after adding texture

Extrusions after correcting using cube projection unwrapping

Extrusions after correcting using smart uv project